CN1117946C - Novel water wall tube block design - Google Patents

Abstract

A water wall heat transfer system comprising tube block and assembly, the assembly comprising a plurality of parallel tubes (91) connected therebetween by a membrane (92), wherein the tube block comprises: a) a base section, and b) a plurality of spaced ridges (3) extending upward from the base section, the upper surface of at least one of the spaced ridges defining a generally horizontal surface, the ridges being spaced to define channels (4) therebetween, the height of at least one of spaced ridges being such that the membrane of the assembly seats thereon, said tube block containing a means for securing the tube block to the tube assembly.

Description

Water wall tube liner block structure

technical field

This invention relates to refractory tube liners which protect metal water wall tubes from hot and highly corrosive furnace gases while maintaining good thermal conductivity.

Background of the invention

Municipal solid waste (MSW) plants incinerate waste in furnaces at temperatures up to about 1644K (2500°F). To recover the valuable energy produced by these MSW plants, water passes through metal water wall tubes adjacent to the furnace and turns into steam due to the high temperature. FIG. 1 shows a conventional water wall tube assembly comprising metal tubes T connected by connecting bulkheads M. As shown in FIG. The steam generated in the tube assembly is then used to start a generator driven by a worm gear. However, MSW plants also produce gaseous products which, if allowed to come into contact with metal pipes, would chemically attack those pipes. In order to prevent these gas products from directly corroding the tubes, and to ensure that these tubes are fully heated, a protective refractory partition is placed between the water wall tubes and the furnace side.

While these refractory partitions help minimize erosion of the metal tubes, their use prevents heat from flowing from the fireside to the water wall tubes. Maximizing heat flow is key to boiler efficiency. If the refractory partitions do not provide adequate heat transfer, the fireside surface of the refractory can become hotter than it was designed for. As the temperature rises, the ash from the burning fuel clings to the surface, creating an insulating layer. Once this occurs, the insulating layer becomes thicker and thicker until heat transfer becomes extremely weak. The "flue gas" above the combustion zone then increases at a velocity and temperature generally above design limits, causing corrosion/erosion downstream of the furnace. Furthermore, the increase of the ash/slag layer can eventually interrupt the ascent of the ash/slag layer and can constitute a major cause of damage to the area of the grate for coaling in the combustion zone. It is well known that the heat transfer efficiency of a refractory partition is inversely proportional to its thickness. For example, a -0.05m (2 inch) thick refractory has only 50% of the heat transfer efficiency of a 0.025m (1 inch) thick partition of the same material. Accordingly, there is a need in the industry to use refractory barrier materials that minimize the thickness of the refractory barrier and preferably be as thin as possible.

Metal water wall tubes and refractory bulkheads are usually hung from the ceiling of the building containing the furnace. Since such water wall tubes and refractory partitions are usually about 30m (100 feet) high, the weight of these suspended water wall tubes and refractory partitions poses a safety problem. Safety considerations, therefore, further motivated the idea of making the refractory partitions as thin as possible.

While the industry has recognized the need for thin refractory partitions, it has also recognized that it is not possible to reduce the thickness of these partitions without compromising performance. In particular, it has been found that reducing the thickness too much (i.e., to about 0.012m (1/2 inch)) will weaken the strength of some points on the diaphragm so that it cannot withstand the stress generated by the pipe at high temperature. Accordingly, the industry typically uses separators having a thickness of at least 0.022 to 0.025 m (0.875 to 1.00 inches) in the smallest part of the cross-section.

MSW Industries has developed several types of refractory construction in its effort to maintain good heat transfer while protecting the metal water wall tubes. One type of refractory is called a "monolithic" refractory. A single piece of refractory material is created by spraying the ceramic material directly onto the interspersed water wall tubes. However, some monolithic refractory materials have been known to suffer from low thermal conductivity, low strength, and difficulty in bonding, which lead to excessive accumulation of slag, which hinders high thermal conductivity and thus reduces efficiency.

Another type of commercially available refractory material is the pipe tile or pipe block construction. Fig. 2 shows a conventional pipe liner structure. The pipe liner is generally a square or rectangular refractory tile (usually not greater than height L0.2 to 0.3m (8 to 12 inches) x width W0.2 to 0.3m (8 to 12 inches) x thickness D0.025m ( 1 inch)), with some changes to its rear surface with channels C and ridges R to suit the structure of the water wall tubes. When these pipe liners are combined in a manner similar to bricklaying, that is, one pipe liner covered with mortar is placed in place and the other pipe liner is placed on top of the first pipe liner Or next to it, a refractory wall is built. This combination continues until the desired wall formation. Usually, a stud S is added to the connecting partition M, or the stud is directly added to the water-cooled wall pipe through the hole H in the ridge of the pipe liner, and the stud (stud) S is fastened by a screw A, so as to Secure the tube spacer and tube assembly, see Figure 3. The channels of the pipe inserts generally do not come into direct contact with the metal pipe to be received. Instead, the channels and tubes are bonded together by an inner layer of mortar (not shown). While the mortar forms a good bond between the tube and the tube liner, its thermal conductivity itself is poor, so heat is prevented from flowing from the furnace to the tube. Overall, tube inserts have the advantages of high strength, good bonding, and higher thermal conductivity compared to monolithic structures.

A conventional water wall tube insert construction includes tube inserts suspended from the top of the tube assembly. For example, EP-A-281863 discloses a water wall tube insert construction in which the tube assemblies have "short tabs" protruding from the tube and the tube insert presses on top of these short tabs. Thus, the short tab becomes the means by which the tube pad is hung. Since the suspended pipe insert is substantially suspended beside the pipe, the lower portion of the pipe insert is not forced into intimate contact with the pipe assembly. Therefore, if there is no mortar between the tube and the tube liner, voids will appear, reducing thermal conductivity and causing corresponding corrosion.

While conventional pipe assemblies consist of metal pipes with a center-to-center spacing of 0.1m (4 inches) and a diameter of 0.076m (3 inches), a single pipe spacer typically measures around 0.2m (7-7/8 inches) in height , about 0.2m (7-7/8 inches) in width, and 0.025m (1 inch) in thickness. This spacing creates a tight fit (i.e., approximately 0.003m (1/8 inch)) between the tube inserts and the tube inserts, which reduces the chance of gaps expanding and impeding heat flow between the tube and tube insert assemblies .

Figure 4 shows the construction of a commercially available refractory pipe liner. This structure is similar to the conventional prior art structure described above, except that there is a groove around the circumference of the tube insert. While this structure has the discussed advantages over a single baffle, it is, however, at least about 0.025 m (1 inch) thick, so has poor heat flow and is heavy.

Another commercial pipe liner construction is the ship-lap construction. The shiplap structure shown in Figure 5 originally used in circulating fluidized bed boilers has an interlocking structure that prevents small particles (such as sand) from penetrating into the gaps between adjacent tube liners. However, the interlocking structure makes the shiplap structure expensive to manufacture. In addition, generally the thickness of the shiplap structure is at least about 0.022 m (0.875 inches). While this greater thickness provides a safety measure against rupture of the pipe liner, it also severely impedes heat flow through the refractory material and makes the pipe liner heavy.

In an effort to improve the thermal conductivity of pipe liner structures, US Patent No. 5,154,139 (Johnson's patent), assigned to Norton Corporation, discloses a pipe liner having a thickness of 0.012 m (1/2 inch) with ribs on the channels piece. As shown in FIG. 6, when the ribbed pipe insert is placed against the pipe insert assembly, the ribs are in contact with the pipe wall. This direct contact allows heat to flow past the low thermal conductivity mortar, thus providing higher thermal conductivity than other conventional tube liner constructions. The structure's thinner thickness (ie 0.012m (1/2 inch)) also increases its thermal conductivity. It was found, however, that the commercial embodiments of Johnson's patent failed in this field. Specifically, in FIG. 6, the crack in the tube liner at the location marked with an "X" started to propagate.

Accordingly, there is a need for a refractory pipe liner that is both lightweight and reliable and has excellent thermal conductivity.

Summary of the invention

According to the present invention, a water-cooled wall heat transfer device is provided, the device includes a tube liner block and a tube assembly, the tube assembly includes several parallel tubes connected with each other by at least one connecting partition, characterized in that, Tube inserts include:

a) a bottom, and

b) Several parallel and spaced ridges protruding from the bottom, the surface of at least one ridge constitutes a surface for receiving the connecting partition, the connecting partition is mounted on the surface of the ridge, and the surface of these spaced ridges Several parallel passages are formed therebetween, and the projection of the raised ridge on which the partition is fixed makes the distance from the surface of the raised ridge to the bottom at least exceed the distance between the lower surface of the partition contacting the surface of the raised ridge and the The distance between the vertical bottom ends of the tubes is such that the parallel tubes are not in direct contact with the channel, thereby eliminating large stress concentrations between these parallel tubes and the channel.

According to the present invention, there is also provided a refractory pipe liner, which includes:

a) a bottom, and

b) Three aligned spacing ridges protruding upwards from the bottom, several channels for placing pipes are formed between the spaced ridges and the ridges, the surface of the central spacing ridge receives the partition plate connecting the pipes, the central spacing The distance between the surface of the ridge and the bottom is at least greater than the distance between the lower surface of the partition contacting the surface of the ridge and the bottom end of the tube in the vertical direction, and the central spaced ridge protrudes from the bottom The distance of the ridge is at least about 0.013m longer than the adjacent ridge.

According to the present invention, a water-cooled wall heat transfer device is provided, which includes a plurality of tube inserts and a tube assembly, the tube assembly includes several parallel tubes connected with each other by at least one connecting partition, characterized in that each A pipe liner includes:

a) a bottom, and

b) Three aligned spacing ridges protruding upwards from the bottom, several channels for placing pipes are formed between the spaced ridges and the ridges, the surface of the central spacing ridge receives the partition plate connecting the pipes, the central spacing The distance from the surface of the ridge to the bottom is at least greater than the distance between the lower surface of the separator contacting the surface of the ridge and the bottom end of the tube in the vertical direction, and the distance between the center and the ridge protruding from the bottom At least about 0.013m longer than the adjacent ridge,

The pipe inserts are rectangular and adjacently assembled with a gap between them, and the gap is at least 0.006m wide.

Brief description of the drawings

Fig. 1 is a perspective view of a conventional pipe assembly.

Fig. 2 is a perspective view of a common pipe liner structure in the prior art.

Figure 3 is a side view of a tube liner assembly secured to a conventional tube liner.

Fig. 4 is a perspective view of a prior art structure.

Fig. 5 is a perspective view of a prior art shiplap structure.

Figure 6 is a side view of a prior art Johnson patent structure.

Fig. 7 is a side view of an embodiment of the present invention.

Figure 8 is a cross-sectional view of an embodiment of the present invention secured to a pipe assembly.

Figure 9 is another embodiment of the present invention in which the stud is covered with a sleeve and a cover is placed over the hole in the pipe block that receives the stud.

Figure 10 is an embodiment of the invention in which the central ridge does not extend the entire length of the tube insert.

Detailed description of the invention

Without going into theory for the moment, it is believed that the commercial embodiment of the Johnson patent suffers from a large stress concentration at the point of contact between the tube pad and the metal tube. By raising the central ridge of the pipe insert so that the connecting bulkhead of the pipe assembly sits on the central ridge (this avoids direct contact between the pipe insert and the metal pipe), it was unexpectedly found that even if the bottom of the pipe insert The thickness is as thin as 0.019m (0.75 inches), and the above damage will not occur.

Referring now to FIG. 8, when the pipe insert 50 is placed against the pipe assembly 60, the studs of the assembly 60 pass through the holes 5 in the center ridge 2, so that the horizontal aluminum plane 3 of the center ridge 2 is fixed to the pipe assembly 60. Connect to the bulkhead 62. Since the height of the central ridge 2 (defined as the distance from the horizontal plane 3 to the front surface of the tube block) exceeds the sum of the thickness of the bottom of the tube block 50 and the radius of the tube 61 , it is impossible for the tube 61 to be in close contact with the channel 4 . The gap between tube 61 and channel 4 is preferably about 0.003 to 0.01 m (1/8 to 3/8 inch). When the studs 63 are tightened, the pipe assembly 60 exerts a force on the channel 4 of the pipe liner 50 filled with mortar (not shown), thereby eliminating the void. The mortar keeps the pipe liner 50 in contact with the pipe assembly 60 in case the connections, ie the studs 63 and the studs, corrode during extended periods of use.

Although the size of the tube inserts will vary according to the final application needs and the tube size of the furnace used, the size of each tube insert is generally 0.15 to 0.3m (6 to 12 inches) in width and 0.15 to 0.3m (6 to 12 inches) in height. 12 inches), the bottom thickness is about 0.016 to 0.019m (0.625 to 0.750 inches). However, in some embodiments, the pipe assembly used has a pipe diameter of 0.076m (3 inches), center spacing of 0.1m (4 inches), and the size of the front surface of the pipe pad is only 0.196m x 0.196m (7- 3/4 by 7-3/4 inches). Without discussing it theoretically, it is believed that the traditional 0.2m×0.2m (7-7/8×7-7/8) inch structure forms a gap of -0.003m (1/8 inch) between each pipe liner, And this gap does not leave enough room for thermal expansion of the tube insert, thereby making the tube insert prone to premature rupture. It is believed that the reduced size of this embodiment of the invention (ie, providing a gap of -0.006 m (1/4 inch) between the individual tube pads) further reduces the stress on the individual tube pads. The thickness 65 of the bottom of the pipe liner 50 is generally about 0.013m to 0.025m (0.5 to 1.0 inch), preferably about 0.013m to 0.019m (0.5 to 0.750 inch). It is believed that the reduction in thickness provides an increase in heat transfer of about 33% over a conventional pipe insert having a thickness of 0.025 m (1 inch). The reduction in size also reduces the weight of the tube pad. In one 0.196m x 0.196m x 0.019m (7-3/4 x 7-3/4 x 0.750 inches) embodiment, the pipe insert consists essentially of oxynitride or nitride bonded silicon carbide, The tube insert weighs only about 28.86N (6.5 lbs).

In some embodiments with three separate ridges, the central ridge is longer than the side ridges, typically 0.013 m to 0.025 m (0.5 to 1.0 inch) longer than the side ridges.

Due to the particularly high temperatures generated in the primary combustion zone (first stage) where tube inserts are used, the tube inserts are generally composed of silicon carbide, preferably oxynitride, nitride or oxide bonded silicon carbide. However, other suitable refractory materials such as aluminum, zirconia and carbon may also be used. In addition to the refractory material itself, the pipe liner includes a binder component with high thermal conductivity. A preferred tube insert composition includes about 80 to 95 percent silicon carbide and about 5 to 20 percent binder such as a nitride or oxide based material. More specifically, the pipe inserts may be made from any of CN-163, CN-183, CN-127 or CN-101, each available from Norton Corporation of Worcester, MA, or It is a comparable refractory material.

Any conventional technique commonly used in the manufacture of pipe inserts may be used to manufacture the pipe inserts of the present invention. In a preferred embodiment, the compound containing silicon carbide particles and binder is put into a dry press and pressed into a wet body, which is then dry-fired in a tunnel kiln with oxygen or nitrogen , become a refractory material.

The refractory slurry used in the present invention may be any suitable composition, preferably one that provides the highest thermal conductivity and heat transfer between the tube inserts and the water wall tubes. A suitable mortar composition is generally based on silicon carbide, and includes a binder that can firmly bond the pipe inserts and metal water wall tubes. In a preferred embodiment, the mortar includes copper metal and silicon carbide. More specifically, the mortar was model MC-1015 copper containing mortar available from Norton Company of Worcester, MA.

Although not shown, additional tube inserts may be placed on adjacent portions of the tube assembly. According to the size of the boiler, the tube liners can generally be placed on the top, bottom and sides to cover most of the water wall tubes in the primary combustion zone when they need to be protected. In a conventional MSW plant, these tube liners are usually used to cover all the water wall tubes damaged by combustion products.

In some embodiments of the present invention, a ceramic sleeve 10 is sleeved on the outside of the stud 63 that fixes the pipe liner 50 to the pipe assembly 60, and a hole cover 11 is placed in the hole in the pipe liner that accommodates the stud 63. on, see Figure 9. It is believed that these variations allow the stud to remain relatively cool, thereby retarding stud corrosion.

In some embodiments, the length of the tube insert ridge 20 does not extend throughout the length of the tube insert, but only extends in the vicinity of the hole 5, see FIG. 10 . It is believed that this arrangement is advantageous for reducing the stress on the tube inserts used in large furnaces in which thermal expansion of long tubes produces an axial non-uniform force on the tube inserts. In some embodiments, the length of the ridge is less than about 50% of the length of the base.

In some embodiments, the change is made by placing a refractory strip (typically (0.013m x 0.165m x 0.015m) (0.5 x 6.5 x 0.625 inches)) at the level of the central ridge of a conventional pipe liner. A conventional pipe liner refractory device. It has been found that this modification also has the desired effect of gently detaching the refractory tube inserts from the surface of the water wall tubes to minimize the greater stresses caused by the greater thermal expansion of the water wall tubes, The integrity of the tube pad assembly is thereby enhanced.

Claims (18)

1. A water-cooled wall heat transfer device, which includes a pipe lining block and a pipe assembly, the pipe assembly includes several parallel pipes connected with at least one connecting partition between each other, it is characterized in that the pipe lining block includes: a) a bottom, and b) Several parallel and spaced ridges protruding from the bottom, the surface of at least one ridge constitutes a surface for receiving the connecting partition, the connecting partition is mounted on the surface of the ridge, and the surface of these spaced ridges Several parallel passages are formed therebetween, and the projection of the raised ridge on which the partition is fixed makes the distance from the surface of the raised ridge to the bottom at least exceed the distance between the lower surface of the partition contacting the surface of the raised ridge and the The distance between the vertical bottom ends of the tubes is such that the parallel tubes are not in direct contact with the channel, thereby eliminating large stress concentrations between these parallel tubes and the channel. 2. The water wall heat transfer device of claim 1, wherein the ridges span the length of the base. 3. The water-cooled wall heat transfer device according to claim 1, characterized in that the extended length of the ridge is less than about 50% of the length of the bottom. 4. The water-cooled wall heat transfer device as claimed in claim 1, wherein a stud protruding from the connecting partition is inserted into a hole passing through the tube liner from the surface of the raised ridge, so that the connecting partition is fixed to The surface of the ridge. 5. The water wall heat transfer device of claim 4, further comprising a hole cover covering the hole at the bottom of the tube insert. 6. The water-cooled wall heat transfer device according to claim 4, further comprising a set of ceramic sleeves outside the studs. 7. The water wall heat transfer device of claim 1 , the gap between said tubes and said channels being between about 0.003 m and 0.01 m. 8. The water wall heat transfer device of claim 1, wherein the thickness of the bottom of the tube pad is between about 0.016m and 0.019m. 9. The water-cooled wall heat transfer device according to claim 1, characterized in that, the intervening ridges on which the connecting partitions are fixed protrude from the bottom longer than the other intervening ridges. 10. A water wall heat transfer device as claimed in claim 9, wherein there is a gap between the tubes and the channels of between about 0.003m and 0.01m. 11. A refractory pipe liner comprising: a) a bottom, and b) Three aligned spacing ridges protruding upwards from the bottom, several channels for placing pipes are formed between the spaced ridges and the ridges, the surface of the central spacing ridge receives the partition plate connecting the pipes, the central spacing The distance between the surface of the ridge and the bottom is at least greater than the distance between the lower surface of the partition contacting the surface of the ridge and the bottom end of the tube in the vertical direction, and the central spaced ridge protrudes from the bottom The distance of the ridge is at least about 0.013m longer than the adjacent ridge. 12. The tube insert of claim 11, wherein the channel is semicircular in shape. 13. The tube insert of claim 11 wherein the ridge spans the length of the base. 14. The tube insert of claim 11, wherein the ridge extends less than about 50% of the length of the base. 15. The tube liner of claim 11, wherein the tube liner further comprises: A hole in the central spaced ridge passes through the bottom of the tube insert from the substantially horizontal surface. 16. The tube insert of claim 11, wherein the thickness of the base is between about 0.013m and 0.025m. 17. The tube insert of claim 11, wherein the base has a thickness of between about 0.016m and 0.019m. 18. A water-cooled wall heat transfer device, which includes a plurality of tube liners and a tube assembly, the tube assembly includes several parallel tubes connected with at least one connecting partition, characterized in that each tube liner Blocks include: a) a bottom, and b) Three aligned spacing ridges protruding upwards from the bottom, several channels for placing pipes are formed between the spaced ridges and the ridges, the surface of the central spacing ridge receives the partition plate connecting the pipes, the central spacing The distance from the surface of the ridge to the bottom is at least greater than the distance between the lower surface of the separator contacting the surface of the ridge and the bottom end of the tube in the vertical direction, and the distance between the center and the ridge protruding from the bottom At least about 0.013m longer than the adjacent ridge, The pipe inserts are rectangular and adjacently assembled with a gap between them, and the gap is at least 0.006m wide.

Images